Blasting cartridge

ABSTRACT

A cartridge ( 10 ) is provided having a receptacle ( 12 ) with propellant ( 14 ) therein and an open end with a stemming device ( 16 ) secured to the open end to form a substantially closed container. The stemming device ( 16 ) is operable to result in radial expansion thereof and has a static member ( 18 ) secured to the receptacle ( 12 ) and a piston ( 20 ) movable, at least partially within the container, relative to the static member ( 18 ) and the receptacle ( 12 ). The cartridge is configured such that ignition of the propellant ( 14 ) causes movement of the piston ( 20 ) to operate the stemming device ( 16 ) and cause radial expansion thereof before the receptacle ( 12 ) ruptures.

FIELD OF THE INVENTION

This invention relates to rock breaking and more specifically tocartridges used for breaking rock.

The term “rock” as used herein covers natural rock and also includesconcrete or similar structures that are to be broken up.

BACKGROUND TO THE INVENTION

Traditional methods of blasting or breaking rock in quarries and minesmake use of high energy explosives, often referred to as detonatingexplosives. High energy explosives crush and pulverise the rock whichcan then be removed for either retrieving the sought after mineralwithin the rock or for disposal of the rock.

The problem with detonating explosives is that the ignition of theexplosive is followed by a violent shockwave which may cause rockfragments to be projected from the explosion site. The projected rockfragments pose a great risk to mine workers, thus commonly requiring alarge area surrounding the blasting site to be cleared. Furthermore, thepulverisation of the rock may create a thick cloud of dust to surroundthe blasting site, making it impossible to work at the site for extendedperiods of time.

The problems associated with the traditional methods of blasting orbreaking rock resulted in the development of rock breaking explosivescommonly referred to as non-detonating explosives. Non-detonatingexplosives function by containing and directing rapidly expanding gaseswithin and against the rock, thereby causing the rock to break withoutthe violent shock wave and pulverisation of the rock.

Non-detonating explosives are used by drilling boreholes into the rock,inserting non-detonating explosive cartridges containing a gasgenerating compound, commonly a propellant, into the boreholes andigniting the cartridges. Prior to ignition of the cartridge, theborehole must be stemmed by packing particulate material, usually sand,into the borehole after insertion of the cartridge. The packedparticulate material keeps the gases created by the cartridge within theborehole once the cartridge has been ignited resulting in high pressurebeing created within the borehole.

A drawback of non-detonating explosives is that adequate stemming of theborehole is of utmost importance, failure of which may cause some of thegas to escape thereby reducing the pressure exerted onto the rock andcausing the cartridge to be less effective. Furthermore, stemming ofboreholes that run at a downward slope may be difficult thus often beingvery time consuming to achieve. Also, stemming material needs to betransported to the blasting site.

A self-stemming cartridge is proposed in U.S. Pat. No. 8,342,095. Oneembodiment of the cartridge disclosed in the patent has a sheath whichis tapered radially inwardly at one end and which houses a gasgenerating compound and a cone. The patent discloses that the cone isforced in the direction of the taper upon ignition of the gas generatingcompound and forces the sheath outwardly, thereby stemming the borehole.

Drawbacks of the disclosed cartridge include the cartridge having a plugat one end which will be ejected from the cartridge prior to stemming,thus causing the stemming operation to stop and the cartridge to beejected from the borehole without breaking any of the rock.

Furthermore, the sheath is of a solid construction. This will permit gasto escape about the periphery of the cone when the sheath flexesoutwardly after ignition and from the gas pressure within the cartridge.It is thus highly unlikely that the cone will operate to expand thesheath. Also, such flexing will cause the development of empty pocketswithin the sheath into which the gas can move, thus causing a drop inpressure within the cartridge and resulting in a cessation of combustionof the gas generating compound.

A further disadvantage of the cartridge disclosed in U.S. Pat. No.8,342,095 is that the sheath is a solid tube and thus unlikely to expandsufficiently to stem the hole. Also, the detonator cord runs betweencone and sheath creating a gap which will permit gas to escape and thusprevent proper working of the cartridge during manufacture and handling.The gap will also permit the propellant to leak out of the cartridge.Furthermore, the detonator must be inserted into the cartridge before itcan be filled with propellant. This will create an inherently dangeroussituation during assembly as there is a possibility of the detonatorigniting the propellant during assembly.

There is no evidence of the cartridges proposed by U.S. Pat. No.8,342,095 being commercially available and the applicant believes thisto be a result of these not being capable of functioning for the reasonsgiven above.

In this specification, “propellant” shall have its widest meaning andinclude any suitable gas producing material, and “igniter” shall meanany device capable of causing the propellant to produce gas.

SUMMARY OF THE INVENTION

In accordance with this invention there is provided a cartridgecomprising a receptacle for holding a propellant therein and having anopen end with a stemming device secured to the open end to form asubstantially closed container, the stemming device being operable toresult in radial expansion thereof and having a static member secured tothe receptacle and a piston movable, at least partially within thecontainer, relative to the static member and the receptacle, andconfigured such that ignition of the propellant causes movement of thepiston to operate the stemming device and cause radial expansion thereofbefore the receptacle ruptures.

Further features of the invention provide for an igniter to be securedwithin the stemming device with an operating cord extendingtherethrough; for the igniter to be preferably located in a socket inthe piston; for the stemming device to be shaped to provide a slidingfit within a borehole; and for the receptacle to be cylindrical.

Still further features of the invention provide for the receptacle to bemade of a plastics material; for the piston to be partly located withinthe receptacle; for the part of the piston located within the receptacleto provide a sliding fit within the receptacle.

Yet further features of the invention provide for the static member tobe secured over the open end of the receptacle; for the static member toprovide a snap fit over the receptacle; for the static member to have aplurality of holes therein for receiving buttons on the receptacle;alternately for the static member to provide a screw fit on thereceptacle.

Further features of the invention provide for a nozzle to extend fromthe piston at the end of the piston that is located within thereceptacle; the nozzle being radially inwardly stepped from the end ofthe piston; and for the nozzle to operatively extend into the propellantheld within the receptacle.

Still further features of the invention provide for the piston andstatic member to have cooperating bearing surfaces, at least one,preferably both, of which is tapered such that relative movement causesradially outward expansion of either the static member or the piston.

Yet further features of the invention provide for a stemming device tobe secured to opposite ends of a tubular receptacle; for either or bothstemming devices to have an igniter associated therewith; and for thestemming devices to be of the same or different configuration to eachother.

According to one aspect of the invention the static member has a taperedbore and at least one longitudinal slit therein to permit radialexpansion thereof.

Further according to this aspect of the invention the static member hasa plurality of circumferentially spaced slits, each slit extendingsubstantially the length of the tapered bore.

According to a further embodiment of the invention the static member ofthe stemming device has a tubular body with a number of ports thereinand an anchor member associated with each port such that movement of thepiston causes radially outward displacement of each anchor member; foreach anchor member to have a lug which extends centrally from one sideof a panel, each lug providing a complementary fit within a port and thepanels configured to extend over a part of the outer surface of thebody; for the ports to be elongate and extend longitudinally along thebody near its free end; for the end of the piston engaging the lugs tobe tapered; and for the free end of each lug to have a complementarytaper to the piston.

The invention also provides a piston for a cartridge substantially asdefined above, the piston having a cylindrical section providing asliding fit within a tubular receptacle and a tapered section which ismovable within an expansion sleeve to cause radial expansion thereof,with a bore extending substantially axially through the piston and anozzle extending from the end of the piston locatable within thereceptacle.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example only withreference to the accompanying representations in which:

FIG. 1 illustrates a side elevation of a cartridge according to a firstembodiment of the invention;

FIG. 2 illustrates a longitudinal section of the cartridge illustratedin FIG. 1;

FIG. 3 illustrates a side elevation of the receptacle of the cartridgeillustrated in FIG. 1;

FIG. 4 illustrates a longitudinal section of the receptacle illustratedin FIG. 3;

FIG. 5 illustrates a side elevation of an expansion sleeve forming astatic member of the cartridge illustrated in FIG. 1;

FIG. 6 illustrates a longitudinal section of the sleeve illustrated inFIG. 5;

FIG. 7 illustrates an end view of the sleeve illustrated in FIGS. 5 and6;

FIG. 8 illustrates a plan view of one of the two parts of a firstembodiment of a piston;

FIG. 9 is a section through the part of FIG. 8;

FIG. 10 illustrates an end view of the part illustrated in FIG. 8;

FIG. 11 illustrates a three-dimensional view of an alternativeembodiment of a piston;

FIG. 12 illustrates a longitudinal section of the piston illustrated inFIG. 11;

FIG. 13 illustrates a side elevation of a cartridge according to asecond embodiment of the invention;

FIG. 14 illustrates an exploded three-dimensional view of a cartridgeaccording to a third embodiment of the invention housing the piston ofFIGS. 11 and 12;

FIG. 15 illustrates a three-dimensional view of the cartridgeillustrated in FIG. 14;

FIG. 16 illustrates a three-dimensional view of a cartridge according toa fourth embodiment of the invention;

FIG. 17 illustrates a longitudinal section of the cartridge illustratedin FIG. 16;

FIG. 18 illustrates an exploded three-dimensional view of the cartridgeillustrated in FIG. 16 housing the piston of FIGS. 11 and 12;

FIG. 19 illustrates an end view of a stemming device of the cartridgeillustrated in FIGS. 16 to 18;

FIG. 20 illustrates a longitudinal section of the stemming device of thecartridge illustrated in FIG. 19;

FIG. 21 illustrates a longitudinal section of a cartridge according to afifth embodiment of the invention;

FIG. 22 illustrates a longitudinal section of a cartridge according to asixth embodiment of the invention;

FIG. 23 illustrates a longitudinal section of a cartridge according to aseventh embodiment of the invention;

FIG. 24 illustrates a longitudinal section of a cartridge according toan eight embodiment of the invention; and

FIG. 25 illustrates a side elevation of a cartridge according to a ninthembodiment of the invention.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

The invention provides a cartridge having an elongate, preferablycylindrical, receptacle which holds a propellant and has an open endwith a stemming device secured to the open end to form a substantiallyclosed container. The stemming device has a static member, typically asleeve, which is secured to the receptacle and a piston which isoperable to move, at least partially within the container, relative tothe static member and the receptacle to result in radial expansion ofthe stemming device. To this end the piston and static member havecooperating bearing surfaces, at least one, preferably both, of which istapered such that relative movement causes radially outward expansion ofeither the static member or the piston.

An igniter is secured within the stemming device, preferably within asocket in the piston, with an operating cord extending therethrough.Ignition of the propellant within the receptacle causes production ofgas within the container which in turn causes movement of the piston.This results in operation of the stemming device and radial expansionthereof.

The receptacle and stemming device are configured to resist ruptureuntil at least partial, preferably complete, operation of the stemmingdevice has been achieved. To this end the receptacle and stemming deviceare made of a rigid plastics material, but any suitable materials can beused. Complete expansion of the stemming device is that permitted by theborehole and compression or deformation of the material of the stemmingdevice.

To achieve proper operation of the stemming device, it is also necessaryto prevent the receptacle from disengaging from the stemming deviceafter ignition of the propellant. One manner of achieving this is forthe stemming device to provide a snap fit over the end of the receptaclethrough radially outward resilient deformation of the stemming deviceover a corresponding formation or formations on the receptacle. With thecartridge in position in a borehole, disengagement can be prevented byensuring a sliding fit of the stemming device in the borehole whichprevents outward deformation thereof. It will be appreciated, however,that the stemming device can be secured to the receptacle in anysuitable manner, including through a screw or bayonet-type fit.

Shaping the stemming device to have a sliding fit within a borehole alsohas the result that minimal radial expansion of the device is requiredfor it to be effective in stemming the borehole. It will be appreciatedthat the receptacle need not have the same outer dimensions as thestemming device. This has the advantage that one receptacle size can beused with different sized stemming devices, each of which provides asliding fit within a different sized borehole.

The two-piece configuration of the cartridge of the invention, thereceptacle with stemming device secured thereto, offers numerousadvantages. Safety is greatly enhanced as the receptacle can be filledwith propellant and transported separately from the igniter and stemmingdevice. These can be fitted on-site so that minimal risk of accidentalignition of the propellant is achieved.

Also, the same stemming device can be fitted to cartridges containingdifferent amounts of propellant and vice versa; the same cartridge canbe secured to different diameter stemming devices intended for use withdifferent borehole diameters. Thus multiple cartridge configurations caneasily be achieved. This provides for both ease of manufacture and easeof use.

Furthermore, the two-piece configuration permits different materials tobe used for the receptacle and stemming device. Thus, the receptacle canbe made of a plastics material which permits it to undergo relativelylarge outward deformation before bursting while the stemming device canbe made of a harder material which is more resistant to deformation andforms and effective plug within the borehole. Gas can thus be containedwithin the receptacle, which expands and conforms to the dimensions ofthe borehole, while the stemming device is being operated by thepressure of the gas.

Various embodiments of a cartridge are now described, by way of exampleonly.

A cartridge (10) is shown in FIGS. 1 and 2 and includes a cylindricalreceptacle, in this embodiment a tube (12), filled with a propellant(14). A stemming device (16) having a static member (18) and a piston(20) movable relative to the static member is secured to the tube (12).In this embodiment the static member (18) is provided by a splitexpansion sleeve and the piston (20) has a cone at one end. The tube(12) and stemming device (16) together define a substantially closedcontainer.

The tube (12) has a domed closed end (22) and is open at the other end(24). At a zone approximately one quarter of the length of the tube (12)from the open end there is a circumferentially extending rib (26) whichis bounded by an inclined surface (28) (FIGS. 3 and 4) and a radialsurface (30).

The sleeve (18) has a securing end (32) and a free end (34) and haslongitudinally extending slits at both ends. More specifically there arefour slits (36) in the securing end (32) and three slits (38) whichextend approximately half way along the sleeve (18) in the free end(34). The slits (36, 38) in both ends are equally spaced around thesleeve. Of course any suitable number of slits can be provided. Forexample, there can be a single slit at the securing end and two slits ormore than three slits at the free end.

Adjacent its securing end (32) the sleeve (18) has an internal groove(40) the shape of which matches that of the rib (26). The section of thesleeve (18) adjacent the free end (34) is formed with circumferentiallyextending, axially spaced ribs (42) between which there are grooves(44). Internally the sleeve (18) has a bore (46) which is cylindrical inshape over a portion of its length and tapering in shape over theremainder. The bore (46) decreases in cross-sectional area in thedirection away from its cylindrical part from the securing end to thefree end. The slits (38) extend the full length of the tapering bore ofthe sleeve and part way along the length of the sleeve which has thecylindrical bore.

The piston (20), in this embodiment, is formed by two parts (48).Turning now to FIGS. 8, 9 and 10, the part (48) illustrated constitutesone half of the piston (20). The part (48) has a flat surface (50) fromwhich two pins (52) protrude and in which there are two sockets (54). Agroove (56) extends along the centre line of the surface (50). At thelarger end the groove (56) enters a central recess (58) in the surface(50).

The cartridge is assembled by placing the tube (12) in a jig in anupright position. The propellant (14) is then poured into the tube (12)and tamped down.

A small quantity of material which produces a flame when ignited, forexample black powder, is then placed in the cavity or socket formed bythe adjacent recesses (58) of the parts (48) of the piston (20) whichare placed face-to-face with the pins (52) in the sockets (54). Thelongitudinal axis of the cone is in the plane of the flat faces of theparts (48) that are in contact. The material can be in particulate formor moulded into the form of a sleeve as shown at (60) in FIG. 2.

An igniter (62) is also placed in the socket. A foil cover (64) isadhered to the piston (20) to close the cavity. An operating cord, inthis embodiment a fuse wire (66), attached to the igniter runs along thebore formed by the registering grooves (56). A thin layer of adhesivecan be applied to the surfaces (50) if desired before they are pressedtogether.

The outer surface of one end of the piston is cylindrical and is steppedso as to form a spigot which slides into the tube (12) when the pistonis pressed down onto the open end of the tube (12). A shoulder at theend of the spigot limits the depth of penetration of the piston into thetube (12). The opposite end is conical and forms a complementary fitwithin the tapering portion of the sleeve (18).

The free end of the fuse wire (66) is threaded through the sleeve (18)(from left to right as viewed in the drawings) and the piston (20)inserted into the tube (12) until it is in the position shown in FIG. 2.

The securing end (32) of the sleeve (18) is then pushed over the openend (24) of the tube (12) until the rib (26) snaps into the groove (40)which locks the tube (12) to the sleeve (18).

The cartridge (10) is now fully assembled and ready for use by pushingit, domed end (22) leading, into a drilled borehole in the rock. If theborehole is horizontal then, using a stick of suitable length, thecartridge is pushed as far along the borehole as is required. If theborehole is vertical the cartridge is just dropped in.

When the igniter (62) is operated, the material in the socket or chamberignites, producing a flame and bursting the foil (64) so that a flamereaches the propellant (14). Ignition of the material in the socketraises the pressure sufficiently to exert some force on the piston (20)to start the stemming procedure. When the propellant (14) ignites, gasis generated which also forces the piston (20) to move relative to thesleeve (18). Movement of the piston (20) within the sleeve (18) causesradial expansion of the sleeve (18) forcing the ribs (42) outwardly intocontact with the surface of the borehole. Whilst there is some gasleakage through the slits (38), it is insignificant and the bulk of gasgenerated is retained in the container provided by the tube (12) andstemming device (16). This eventually causes the tube (12) to burstreleasing the gas into the borehole. The grip between the ribs (42) inthe expanded condition of the sleeve (18) and the rough surface of thedrilled borehole prevents the cartridge (10) from moving along theborehole and traps the gas within the borehole causing the rock tofracture as a result of the high pressure created by the gas.

The cartridge has been found to be highly effective in breaking rockwithout the need for any additional stemming material. It thuscompletely eliminates the need for the time-consuming and costlyprocedure of using stemming material.

The stemming device (16) remains attached to the tube (12) duringstemming as the sliding fit between the sleeve and borehole preventssufficient radial expansion for the sleeve (18) to disengage from therib (26). Also, the portion of the sleeve (18) which surrounds the endof the tube (12) provides circumferential reinforcement which assists inpreventing radial expansion of the tube in that area and the consequentescape of gas between the piston and tube. It is thus preferable thatthe sleeve extend over the tube to at least the depth of the piston inthe tube, preferably further. Alternatively, some form ofcircumferential reinforcement, such as a thickening of the sides wallcan be provided to assist in preventing radial expansion of the tubeabout the piston.

The cylindrical end of the piston acts to keep the piston aligned withinthe sleeve during its travel. This helps ensure proper expansion of thestemming device and avoids potential misalignment which may occur with apurely conical piston moving within a tapered bore. Misalignment canresult in incomplete stemming and also in gaps being formed between thepiston and sleeve which permit gas to escape therethrough. Both of thesesituations would have an negative effect on the performance of thecartridge.

It will be appreciated that many embodiments of a cartridge exist whichfall within the scope of the invention, particularly regarding theconfiguration and operation of the stemming devices, the method by whichit is secured to the receptacle and the configuration of the receptacle.

For example, as shown in FIGS. 11 and 12, the piston (70) can be ofone-piece construction and have a cylindrical body (68) with a first end(71) and a second end (72). A nozzle (74) extends axially from the firstend (71) and is provided by a radially inwardly stepped projection. Thesecond end (72) is inwardly tapered from a radially outwardly steppedshoulder (76). A bore (78) extends axially through the piston (70) andis radially enlarged adjacent the first end (71) to form a chamber (80).Flame producing material, for example black powder, is placed into thechamber (80) at the first end (71) of the piston (70) as describedabove.

This piston configuration has been found to be particularly effective.The additional flame producing material produces a sustained, hightemperature flame. This permits a standard igniter to be used in thecartridge. Such igniters have been found to produce erratic propellantignition when used on their own, particularly with relatively largepropellant volumes. Furthermore, although the precise mechanism is notfully understood, the nozzle appears to assist in creating a flame jetwhich is highly effective in initiating and maintaining propellantignition.

FIG. 13 illustrates a second embodiment of a cartridge according to theinvention. In this embodiment buttons (90) are provided on the surfaceof the tube (12.1). Each button has an inclined camming surface and alocking surface which intersects the camming surface. The sleeve (18.1)has complementary holes (92) for receiving the buttons (90). As the end(94) of the sleeve (18.1) is pressed onto the tube (12.1) it rides upover the camming surfaces until the holes (92) are reached. With theholes (92) properly aligned, the buttons (90) snap into the holes (92).The locking surfaces of the buttons (90) engage the peripheries of therespective holes (92) to prevent the sleeve (18.1) from being pulledback off the tube (12.1).

Alternatively, as shown in FIGS. 14 and 15, the sleeve (18.2) can haveholes (92.2) for receiving buttons (90.2) with corresponding slits (96)extending from the end (98) of the sleeve (18.2) centrally into eachhole (92.2). With the piston (70) in position in the open end (24.2) ofthe tube (12.2), the end (98) of the sleeve (18.2) is forced over theclosed, rounded end (22.2) of the tube (12.2) until the buttons (90.2)locate within the respective holes (92.2). No further movement of thesleeve in the direction of the open end of the tube is permitted by thisarrangement.

This configuration has been found to work particularly well as itfacilitates assembly of the cartridge and eliminates the potential ofthe sleeve being separated from the tube during expansion of thestemming device.

FIGS. 16 to 20 illustrate a cartridge according to a further embodimentof the invention. In this embodiment a screw thread (100) at the openend of the tube (12.3) cooperates with a complementary thread (102)provided internally of the sleeve (18.3) to secure the sleeve to thetube.

The sleeve (18.3) has three elongate, longitudinally extending,circumferentially spaced ports (104) at its free end (106) and an anchormember (108) is associated with each port (104). Each anchor member(108) has a lug (110) which extends centrally from one side of a panel(112). On the opposite side, the panels each having axially spaced ribs(42.2) between which there are grooves (44.2). Each lug (110) provides acomplementary, sliding fit within a port (104) with each panel (112)providing a complementary fit over part of the outer surface of thesleeve (18.3).

The free end (114) of each lug (110) abuts the piston (70.2) and has ataper complementary thereto. When the cartridge is ignited, the piston(70.2) moves towards the sleeve (18.3), causing the tapered end of thepiston (70.2) to engage the lugs (110) of the anchor members (108). Thisdisplaces the anchor members (108) outwardly from the sleeve (18.3)resulting in radial expansion of the stemming device.

It will be appreciated that the stemming device may be varied in designto allow for the radial expansion and engagement with the walls of theborehole. For example, the sleeve (18) need not have slits to permitexpansion, but could have lines of weakness or any other suitableconfiguration. In particular, it is not required that both the staticmember (18) and piston (20, 70) have tapered or inclined bearingsurfaces. It is simply required that radial expansion occurs uponrelative movement of the piston (20, 70) and static member (18).

For example, as shown in FIG. 21, the piston (120) could have a radiusedbearing surface (122) which moves within the tapered cavity (124) of thesleeve (126) to cause radial expansion of the sleeve (126).

Referring to FIG. 22, the piston (130) can provide a sliding fit overthe end of the tube (12) and within the static member (132) which is inturn secured to the tube (12).

As shown in FIG. 23, the static member (140) could be secured to a post(142) extending centrally within the tube (12) and integral therewith.The static member (140), in this embodiment, has a bearing surface (144)which tapers outwardly from the post (142) and cooperates with acomplementary bearing surface (146) on the piston (148), a cylindricalbody which slides within the tube (12) over the post (142). Ignition ofthe propellant causes the piston (148) to move against the static member(140) with a resultant radially outward expansion of the piston (148).

It is also possible for rotational movement to be achieved and employedby the stemming device. For example, as shown in FIG. 24, the piston(200) has one end (202) which is a sliding fit within the tube (12). Theopposite end (204) has a smaller diameter which is tapered. Intermediatethe ends (202, 204) the piston is radially thickened (206) and providedwith a course screw thread which cooperates with a complementary thread(208) provided internally of the static member (210) which has asleeve-like configuration and fits over the tube (12) in a manneranalogous to that described with reference to FIGS. 1 and 2. The thread(208) runs from about the end of the tube (12) to an inward thickening(212) which provides, at one end (214), a bearing surface complementaryto, and abutting, the end (204) of the piston (200). The opposite end(216) of the thickened portion (212) is similarly, outwardly taperedfrom the centre. A shaft (218) extends centrally from the end (204) ofthe piston (200), through a passage (220) in the thickened portion(212). The end (222) of the shaft is screw threaded and has acomplementarily threaded nut (224) secured thereto. The nut (224) has alug (226) extending from one side which registers in a longitudinallyextending groove (not shown) in the end (228) of the static member (210)to prevent rotation thereof. The internal end (230) of the nut (224)abuts the end (216) of the thickened portion (212) and iscomplementarily tapered to provide a conical surface.

In use, gas produced by the propellant forces the piston (200) towardsthe static member (210) causing it to rotate through engagement with thescrew thread. Rotation of the piston (200) also results in rotation ofthe shaft (218) which is threaded to cause the nut (224) to be drawninwardly towards the piston (200) and static member (210). This alsoapplies an axial force to the opposite end (216) of the thickenedportion (212) which results in its radially outward displacement. Thethickened portion (212) is thus subject to compression between thepiston (200) and nut (224) and undergoes rapid and effective radialexpansion. To effect radial expansion the thickened portion may besegmented.

Clearly, other configurations exist which make use of a rotating piston.For example, the piston could be made to rotate on a post extending fromthe tube, similarly to that illustrated in FIG. 23, and to drive intothe static member with a screwing action to cause radial expansion.

A very important benefit of the cartridge of the invention, in largepart a result of the two-piece construction, is that it can be providedwith a stemming device (16) at opposite ends of a receptacle (300), asillustrated in FIG. 25. Of course the receptacle (300) would, in thisembodiment, be tubular and open at both ends. A removable membrane, orone that can easily be ruptured can be provide over one or both ends toretain the propellant in the tube until the stemming devices have beenfitted. Such a cartridge finds application in relatively thinstructures, such as walls, where the end of the borehole may not providesufficient resistance to the expanding gas of the propellant foreffective blasting to occur.

Any suitable stemming device, or combination of stemming devices,including those described above, can be used in such a cartridge. Anigniter can be associated with each stemming device if desired, but onlyone igniter will often be sufficient. In such cases, the stemming devicewhich does not have an igniter or operating cord associated with it willeither have no passage or socket for these or will have these plugged.Once again, the configuration of the stemming device, that of a staticmember and piston, means that it is a simple matter to provide differentpistons with the same static member.

Clearly, expansion of the stemming device can be achieved in many otherways and many other embodiments of a cartridge which fall within thescope of the invention will be apparent to those skilled in the art.

1. A cartridge comprising a receptacle for holding a propellant thereinand which has an open end, and a stemming device operable to result inradial expansion thereof having a piston movable relative to a staticmember, wherein the stemming device is secured to the open end of thereceptacle to form a substantially closed container, with the staticmember secured to the receptacle and the piston movable at leastpartially within the container such that ignition of the propellantcauses movement of the piston to operate the stemming device and causeradial expansion thereof before the receptacle ruptures.
 2. A cartridgeas claimed in claim 1 wherein the cartridge has an igniter securedwithin the stemming device with an operating cord extendingtherethrough.
 3. A cartridge as claimed in claim 2 wherein the igniteris located in a socket in the piston.
 4. A cartridge as claimed in claim1 wherein the piston is partly located within the receptacle.
 5. Acartridge as claimed in claim 4 wherein a nozzle extends from the end ofthe piston located within the receptacle.
 6. A cartridge as claimed inclaim 1 wherein the static member is secured over the open end of thereceptacle.
 7. A cartridge as claimed in claim 6 wherein the staticmember has a plurality of holes therein for receiving buttons on thereceptacle.
 8. A cartridge as claimed in claim 1 wherein the piston andstatic member have cooperating bearing surfaces, at least one of whichis tapered such that relative movement causes radially outward expansionof either the static member or the piston.
 9. A cartridge as claimed inclaim 8 wherein the static member has a tapered bore and at least onelongitudinal slit to permit radial expansion thereof.
 10. A cartridge asclaimed in claim 9 wherein the static member has a plurality ofcircumferentially spaced slits, each slit extending substantially thelength of the tapered bore.
 11. A cartridge as claimed in claim 1wherein the static member of the stemming device has a tubular body witha number of ports therein and an anchor member associated with each portsuch that movement of the piston causes radially outward displacement ofeach anchor member.
 12. A cartridge as claimed in claim 11 wherein eachanchor member has a lug which extends centrally from one side of apanel, each lug providing a complementary fit within a port and thepanels configured to extend over a part of the outer surface of thebody, for the end of the piston engaging the lugs to be tapered, and forthe free end of each lug to have a complementary taper to the piston.13. A cartridge as claimed in claim 1 wherein a stemming device issecured to opposite ends of a tubular receptacle.
 14. A piston for acartridge as claimed in claim 1, wherein the piston has a cylindricalsection providing a sliding fit within a tubular receptacle and atapered section which is movable within an expansion sleeve to causeradial expansion thereof, with a bore extending substantially axiallythrough the piston and a nozzle extending from the end of the pistonlocatable within the receptacle.